Paper mills have for many years made extensive use, for the screening of paper making stock, of screen apparatus embodying a cylindrical perforate screen member defining screening and accepts chambers on the opposite sides thereof in a closed housing and provided with a rotor member which operates in one of the chambers to keep the screen perforations open and free from solid materials tending to cling to the screen surface. Commonly, the stock or furnish is delivered to the screening chamber adjacent the end of the screen member, and the material rejected by the screen member is collected and discharged from the opposite end of the screen member.
The assignee of this invention has manufactured and sold many such screens, originally in accordance with Staege U.S. Pat. No. 2,347,716, and more recently in accordance with Martindale U.S. Pat. No. 2,835,173, the latter construction being characterized by a rotor comprising bars or vanes of air-foil section in closely spaced but non-contacting relation with the surface of the screen member. Similar screens have been marketed for some years in competition with those of the assignee of this invention, in accordance with other patents such, for example, as Cannon et al U.S. Pat. No. 2,975,899, Lamort U.S. Pat. No. 3,617,008 and Holz U.S. Pat. No. 3,581,983.
The art has also experimented widely with detailed variations in screens of the above type, including variations in the size, spacing and configuration of the perforations in the screen member and also in the vane shape and in other forms of rotor. For example, such screens have been offered in recent years wherein the rotor is a drum-like member provided with multiple bumps or other offset portions over its surface. Typical such constructions are shown in Clarke-Pounder U.S. Pat. No. 3,363,759 and Bolton et al U.S. Pat. No. 3,726,401.